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Pre-treatment with cyclophosphamide or OX40 (CD134) costimulation targeting regulatory T cell function enhances the anti-tumor immune effect of adoptively transferred CD8+ T cells from wild-type mice TOMOYUKI UEKI, SATOSHI MURATA, NAOMI KITAMURA, EIJI MEKATA and TOHRU TANI Department of Surgery, Shiga University of Medical Science, Seta Tsukinowa, Otsu City, Shiga 520-2192, Japan Received December 31, 2008; Accepted April 21, 2009 DOI: 10.3892/mmr_00000146 Abstract. Regulatory T cells (Tregs) are a major obstacle to the establishment of effective cancer immunotherapy. As mediators of immune tolerance, they are a critical target for pre-conditioning for adoptive immunotherapy. Here, we show that pre-treatment with cyclophosphamide or agonistic anti-OX40 mAb augments the anti-tumor immune effect of adoptive CD8+ T cell therapy in a clinically relevant wild-type model, as opposed to a TCR-transgenic mouse model. Tumor antigen-stimulated CD8+ T cells (7x106), including a small number (2.17x105) of tumor antigen-specific effector CD8+ T cells, were transferred into tumor-bearing mice. A response was detected in the adoptively transferred antigen-specific CD8+ T cells, but was insufficient for the eradication of the established tumor. However, pre-treatment with cyclophosphamide to reduce Tregs was shown to enhance the anti-tumor immune effect of the adoptively transferred CD8+ T cells. Moreover, we demonstrated for the first time that pre-treatment with OX40 costimulation, with the aim of nullifying Tregmediated suppression, maintained the tumor-specific immune response of adoptively transferred CD8+ T cells, resulting in the eradication of the established tumor. These findings suggest that pre-conditioning with the aim of depleting Tregs is a useful strategy for adoptive cancer immunotherapy. Introduction Several strategies for immunotherapy have been evaluated in cancer patients; however, no consistent clinical response has been observed to date. One of the main reasons for this may be an immunological tolerance to tumor (self-) antigens. Tregs play a major role in tolerance to self-antigens. As tumorassociated antigens are derived from self-antigens, Tregs may be responsible for the observed lack of anti-tumor immune
_________________________________________ Correspondence to: Dr Satoshi Murata, Department of Surgery, Shiga University of Medical Science, Seta Tsukinowa, Otsu City, Shiga 520-2192, Japan E-mail:
[email protected] Key words: murine model, T cells, costimulation, tumor immunity
response (1). Indeed, their removal enhances anti-tumor immune response in animal models (1). Thus, one possible strategy for the successful immunotherapeutic treatment of cancer is the depletion of Tregs via pre-conditioning prior to immunotherapy. Cyclophosphamide is an alkylating chemotherapeutic agent used to treat various types of cancer. Cyclophosphamide decreases the number of Tregs in tumor-bearing rats (2) and inhibits their suppressive abilities (3). Several pre-clinical studies have shown that low doses of cyclophosphamide enhance the anti-tumor activity of adoptively transferred T cells (4-6) or of tumor vaccines (7,8). OX40 (CD134) is a member of the TNF receptor family that is transiently expressed on effector T cells after T cell receptor (TCR) triggering. OX40 costimulation enhances the effector function, memory development and survival of CD4+ or CD8+ T cells, resulting in the enhancement of anti-tumor immune effects in vivo (9-12). OX40 signaling inhibits the Treg-mediated suppression of effector CD4+ T cells without reducing the number of Tregs (13,14), while the OX40mediated abrogation of Treg function boosts adoptive immune response and increases tumor rejection (15). However, little is known regarding the efficacy of pre-treatment using OX40 costimulation followed by adoptive T cell therapy on Tregmediated suppressive function. Clonal CD8+ T cells isolated from tumor antigen-specific TCR-transgenic mice have generally been used in murine models of adoptive T cell therapy. This is because a number of tumor antigen-specific T cells can be obtained from these mice, and the response of the adoptively transferred T cells can easily be detected in the recipients, whereas from wild-type mice it is difficult to obtain a sufficient number of Ag-specific CD8+ cells for the detection of immune effect. However, for the clinical application of new strategies for adoptive T cell therapy, an evaluation of anti-tumor immune effect using adoptively transferred T cells from wild-type animals is, if feasible, preferable. The present study evaluated the availability of antigen-specific CD8+ T cells from wild-type tumor-bearing mice for adoptive T cell therapy of an established tumor. The results revealed that pre-treatment with cyclophosphamide or OX40 costimulation to inhibit Treg-mediated suppressive function promoted the effector function of CD8+ T cells adoptively transferred from tumor-bearing wild-type mice, and
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resulted in the eradication of the established tumor in the recipient mice. Materials and methods Animals and cell lines. FVB/N mice were commercially obtained from The Jackson River Laboratory (USA). The animals were housed under pathogen-free conditions at the Shiga University of Medical Science, Japan. Experiments involving the use of the mice were performed in accordance with protocols approved by the Animal Care and Use Committee of Shiga University of Medical Science. Non-transgenic (NT) cells were derived from the spontaneous mammary tumors of female HER2/neu transgenic mice as previously described (16). This NT cell line stably overexpresses rat HER2/neu cDNA. NT cells were grown in defined breast media and maintained at 37˚C in 5% CO2. NIH-3T3 cells were grown in 3T3 media at 37˚C in 10% CO2. 3T3 neu cells derived from NIH-3T3 cells overexpressing rat HER2/neu proto-oncogene were grown in 3T3 media with 0.3 μM methotrexate at 37˚C in 10% CO2. The 3T3 neu cells were genetically modified to express murine cytokine GM-CSF using retroviral vector MFG as previously described (9,16,17), resulting in a 3T3-neu/GM cell line.
Adoptive immunotherapy. The FVB recipient mice were injected s.c. with 5x106 NT2.5 tumor cells in the mammary fat pad on day 3, and i.p. with 100 mg/kg cyclophosphamide, 300 μg anti-OX40 mAb or 300 μg control IgG on day 2. Seven million HER2/neu-primed CD8+ T cells suspended in 400 μl PBS were adoptively transferred into the recipient mice on day 0. Splenocytes and lymphocytes were harvested from the recipient mice on day 6, and ICS was performed. Tumor size was measured and recorded every 3 or 4 days according to the diameter along the orthogonal axes. Population of CD4+CD25+Foxp3+ regulatory T cells in tumorinoculated mice following cyclophosphamide or anti-OX40 mAb administration. FVB mice were injected s.c. with 5x106 NT2.5 tumor cells in the mammary fat pad on day 1, and i.p. with 100 mg/kg cyclophosphamide, 300 μg anti-OX40 mAb or 300 μg control IgG on day 0. Splenocytes and lymphocytes were harvested, and red blood cells were lysed on days 0, 2, 4 and 6. Subsequently, the population of CD4+CD25+Foxp3+ regulatory T cells was investigated using a flow cytometer. Statistical analysis. Data analysis was performed using the Student's t-test. Results
Antibodies and reagents. The RNEU420-429 (PDSLRDLSVF) and NP118-126 (RPQASGVYM) peptides (>95% purity) were synthesized and generously donated by the Oncology Peptide Synthesis Facility at Johns Hopkins University. Agonistic anti-OX40 mAb was produced from OX86 hybridoma cell lines. Purified rat IgG was used as a control Ab (Sigma). The antibodies were reconstituted in PBS, and were administered by i.p. injection at a dose of 300 μg per mouse in 400 μl PBS. APC anti-mouse CD8a, PE rat anti-mouse IFN-Á, FITC antimouse CD4 and PE anti-mouse CD25 were obtained from BD Pharmingen. APC-conjugated anti-mouse/rat Foxp3 and Foxp3 staining buffer sets were obtained from eBioscience. Image cytometry on sections (ICS) was performed as previously described (7) using a Cytofix/Cytoperm™ Plus (with Golgistop™) kit from BD Biosciences. Cyclophosphamide obtained from Sigma Chemical Co. was reconstituted in 400 μl PBS, and administered by i.p. injection at a dose of 100 mg/kg body weight. CD8+ T cells were isolated from splenocytes and lymphocytes by magnetic separation using Dynabeads FlowComp™ mouse CD8 (Invitrogen). Cells were collected using the BD FACSCalibur flow cytometer (BD Biosciences). Data were analyzed using Cell Quest (BD Biosciences) and FlowJo (Tree Star Inc.) software. Immunization of donor mice. Female FVB mice (6-8 weeks old) were injected s.c. with 5x106 NT2.5 tumor cells in the mammary fat pad on day 3, and with 3x106 3T3 neu/GM vaccine cells divided equally between two forelimbs and one hind limb on day 0. T cells were isolated from splenocytes and lymphocytes by nylon wool columns on day 7. These cells were incubated at 37˚C in 5% CO2 for 2 days with T2Dq cells pulsed with RNEU420-429 at a responder to stimulator ratio of 5:1. After 2 days of stimulation, the CD8+ T cells were isolated by magnetic separation using Dynabeads FlowComp mouse CD8. The purity of CD8+ T cells was confirmed to be >95%.
Generation and expansion of HER2/neu-specific CD8+ T cells for adoptive immunotherapy. As described above, for clinically relevant immunotherapy it is more relevant to use a wild-type mouse model than an antigen-specific TCR-transgenic mouse model when evaluating anti-tumor efficacy. However, these mice have a lower number of Ag-specific CD8+ T cells, and in adoptive cytotoxic T lymphocyte (CTL) therapy for tumor eradication, the efficacy of the anti-tumor immune effect is dependent on the number of tumor-antigen-specific CTLs transferred; the greater the number of CTLs, the greater the efficacy. Consequently, antigen-specific CD8+ T cells were generated in vaccinated tumor-bearing wild-type mice and expanded with antigen-specific re-stimulation in vitro. HER2/neu-specific CD8+ T cells, which were confirmed by IFN-Á-producing CD8+ T cell response to RNEU420-429, a HER2/neu immnodominant peptide (16), were generated in the tumor-bearing FVB/N wild-type mice treated with HER2/neutargeted vaccine (16,17). T cells from these vaccinated FVB/N wild-type mice were re-stimulated with T2Dq cells pulsed with RNEU 420-429. Subsequently, the HER2/neu-specific CD8 + T cells were expanded. The maximum frequency of HER2/ neu-specific CD8+ T cells was 3.14±0.276% on day 2 after re-stimulation in vitro (Fig. 1). Consequently, CD8+ T cells re-stimulated with RNEU420-429 for 2 days in vitro were used for the adoptive transfer experiments. Persistence of effector function of adoptively transferred CD8+ T cells with pre-conditioning for Treg depletion. A total of 7x106 in vitro re-stimulated CD8+ T cells from vaccinated wild-type FVB/N mice were adoptively transferred into tumorbearing recipient FVB/N mice with control rat-IgG. More HER2/neu-specific CD8+ T cells were detected in tumorbearing recipient mice with T cell transfer than in tumorbearing mice without T cell transfer (Fig. 2A), indicating that
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Figure 1. Isolated T cells from immunized mice were activated by the stimulation of T2Dq cells pulsed with RNEU420-429. Representative data of three individual experiments are shown. There were three mice in each group. Error bars represent the SD of triplicate assays.
a small number (~2.17x105 cells) of HER2/neu-specific CD8+ T cells persisted in an immune response to HER2/neu in the tumor-bearing recipients. The recipient mice were pre-conditioned with cyclophosphamide or anti-OX40 mAb to inhibit the Treg-mediated suppression of T cells. Antigen-primed CD8+ T cells were transferred 2 days after pre-conditioning, and the persistence of antigen-specific CD8+ T cells was observed 6 days after the adoptive transfer of CD8+ T cells. T cell-transferred recipient mice pre-treated with cyclophosphamide administered i.p. retained significantly more HER2/neu-specific CD8+ T cells than the mice without pre-treatment (Fig. 2B). T celltransferred recipients pre-treated with anti-OX40 mAb administered i.p. also retained significantly more HER2/neuspecific CD8+ T cells than the mice without pre-treatment (Fig. 2C). Tumor-bearing mice treated with cyclophosphamide or anti-OX40 mAb did not generate HER2/neu-specific CD8+ T cells (Fig. 2B and C). This indicates that the frequency and function of a small number of adoptively transferred HER2/ neu-specific CD8+ T cell clones were maintained in vivo. Enhanced anti-tumor immune effects of adoptively transferred HER2/neu-specific CD8+ T cells with the pre-conditioning of Tregs in established tumor-bearing recipient mice. The antitumor efficacy of adoptive CTL therapy was examined in the tumor-bearing recipients with or without pre-treatment for the inhibition of Treg-mediated suppression. The recipient mice with adoptively transferred CD8+ T cells alone exhibited significantly delayed tumor growth in comparison to the mice without treatment (IgG i.p. alone). However, alone the adoptively transferred CD8+ T cells were incapable of eliminating the tumors entirely (Fig. 3). Mice pre-treated with cyclophosphamide alone exhibited significantly inhibited tumor growth in comparison with the mice without pretreatment. In contrast, mice pre-treated with anti-OX40 mAb alone did not exhibit anti-tumor effects. This suggests that cyclophosphamide acts as an anti-tumor agent, while antiOX40 mAb has no anti-tumor efficacy on its own (Fig. 3). However, mice pre-treated with cyclophosphamide or antiOX40 mAb into which CD8+ T cells were then adoptively transferred demonstrated significantly inhibited tumor growth
Figure 2. Pre-treatment with cyclophosphamide or anti-OX40 mAb augments the immune effects of adoptively transferred T cells. Representative data of three individual experiments are shown. There were three mice in each group. Significance was evaluated using the Student's t-test. *P
